Altitude control system



Sept. 22, 1953 F. MARTINDELL. 2,

ALTITUDE CONTROL SYSTEM FiledMarch 25, 1949 s Sheets-Sheet 1 'AssmuCONTROL CENTER KEY INVENTOR I-RANK MARTINDELL f-vyl ATTORNEY Sgpt. 22,1953 F. MARTINDELL ALTITUDE CONTROL SYSTEM 5 Sheets-Sheet 2 Filed March23, 1949 INVENTQR FRANK MARTINDELL ATTORNEY FIG. 2

CONTROL TOWER Sept. 22, 1953 F. MARTINDELL 2,653,307

ALTITUDE CONTROL SYSTEM Filed March 25, 1949 5 Sheets-Sheet 3 In q ijFIG. 3 o 7| 3 v I '2 J I F I 2 l3 TO r-'-- ALARM CIRCUIT n3 INVENTORATTORNEY 5 Sheets-Sheet 4 Filed March 23, 1949 IZZ ALARM CIRCUIT FIG. 5

INVENTOR FRANK MARTINDELL 8Y2 m 2 I ATTORNEY FIG. 2

FIG.

FIG.

FIG.

Sept. 22, 1953 F. MARTINDELL ALTITUDE CONTROL SYSTEM 5 Sheets-Sheet 4Filed March 25, 1949 IZZ FIGL4 FIG. 5

INVENTOR FRANK MARTINDELL Z2 WM ATTORNEY FIG. 2

FIG. 4

FIG.

FIG.

Sept. 22, 1953 F. MARTINDELL. 2,653,307

ALTITUDE CONTROL SYSTEM Filed March 23, 1949 5 Sheets-Sheet 5 FIG. 7

FIRST CHARACTER SECOND CHARACTER ART STOP 1s T R 1;,

AUX. CAM

TRANSMIT R RUNNING PUSH BUTTON 32 CLUTCH COIL RI RELAY R2 RELAY ASSIGNCONTROL LIGHTS CANCEL INVENTOR FRANK MARTINDELL ATTORNEY Patented Sept.22, 1953 ALTITUDE CONTROL SYSTEM Frank Martindell, Western Springs,11]., assignor to Teletype Corporation, Chicago, 111., a corporation ofDelaware Application March 23, 1949, Serial No. 83,000

11 Claims. 1

This invention relates to aircraft control systems and more particularlyto systems for indicating and controllin the altitudes of a plurality ofaircraft.

The present invention is designed particularly for use in situationswhere a control center takes over the control of an airplane when itreaches a certain distance from its destination and thereafter when theairplane gets closer to the landing field the control centerrelinquishes control of the airplane to the control tower whichsupervises the landing of the plane.

The present system consists generally of two units at the control centerand two units at the airport control tower.

The two units at the center are similar in design and function to thetwo units at the tower. The first of each set of units is a push buttonand light panel located at an operators position. lhe second unit ofeach set consists of a selective control unit of the type shown in thecopending application of W. J. Zenner, Serial No. 739,747, filed April7, 1947, now Patent No. 2,568,264, dated September 18, 1951, togetherwith its associated relays and signal transmitting mechanism. Thedisclosure of this Zenner patent is hereby incorporated by referenceinto the present disclosure and. should be referred to for a completeunderstanding of the selective control units.

The push button and light panel, or indicator unit at the center andtower consists, at each 1000 foot level, of a button to assign anairplane to that particular level, a button to cancel the assignment,and associated red and green indicator lights.

Upon the approach of an airplane to a landing field, at some pointmidway between the points of departure and destination, the control ofthe airplanes flight is taken over by a traffic center. The trailiccenter contacts the plane by radio and posts data covering the airline,flight number, expected time of arrival, etc. on a control board in aslot opposite the level at which the plane is flying. When the planearrives within a certain distance from the landing field, the trafficcenter operator assigns it a level by radio, and at the same timedepresses an assign button associated with the level in question.Depression of this assign button causes the corresponding green light toilluminate at the center board and the corresponding red light toilluminate at the tower board.

When the airplane approaches close enough to the landing field to comeunder the direction of the tower, the tower operator calls the plane toadvise it whether or not it is to wait or to make an immediate landing.At this time the tower operator depresses the assign buttoncorresponding to the level at which the plane is flying to transfer thecontrol of the plane from the center to the tower. This transfer isindicated by a change in the arrangement of the lights; the green lightat the center being extinguished and simultaneously therewith thecorresponding red light being illuminated, the red light at the towerbeing extinguished and the corresponding green light being illuminated.Whenever a red light is displayed for a particular level on the centerpanel it indicates that control over an airplane flying at that level isin the hands of the tower, and when a red light is displayed for aparticular level on the tower board the tower operator knows that thecenter controls an airplane flying at that level.

The tower, having obtained control over the airplane, then proceeds toassign successively lower levels to the plane as it descends until itlands. As the plane leaves a particular level and enters a new one, thetower operator cancels the assignment for the old level therebyextinguishing lights on both boards for that level, and at the same timeassigns new levels thereby causing the illumination of the red light atthe center and green light at the tower corresponding to the new levels.I

The principal object of the invention is therefore to provide anaircraft altitude control system which is simple to operate and which atall times informs the control center operator and control tower operatorwhether or not an airplane is assigned to a particular altitude and ifassigned, which control office has control of the airplane.

Another object of the invention is to provide an aircraft altitudecontrol system whereby the display of an illuminated red light on acontrol panel indicates that the particular level is occupied by anairplane which is under the control of a difierent control officewhereas the display of an illuminated green light on a control panelindicates that the particular level is occupied by an airplane which isunder the control of the oifice in which the control panel is located.

Another object of the invention is to provide an aircraft altitudecontrol system wherein the assignment of a level to an airplane can onlybe canceled by the control office having control of the airplane.

These objects and others will be apparent and the invention will beunderstood more readily from the following detailed description whenread in conjunction with the accompanying drawings wherein Figs. 1-4 areschematic circuit diagrams showing the system as contemplated by theinvention;

Fig. shows the manner in which Figs. 1-4 should be assembled;

Fig. 6 shows one of the control panels used in the invention; and

Fig. '7 is a timing diagram of the signal transmitting mechanism.

In the drawings Figs. 1 and 3 represent the apparatus and circuits atthe control center and Figs. 2 and 4. represent the apparatus at thecontrol tower. The center and the tower are each provided with aselective control unit designated by reference numerals II and I2. For adetailed description of these selective control units II and I2,reference should be had to the aforementioned patent of W. J. Zenner. Itwill sufiice for the description of the present invention to state thatthe selective control units H and I2- are each provided respectivelywith a receiving magnet 83 and I4 which are of the type illustrated inFig. 2 of the Zenner patent and are therein designated by the referencenumeral I4. In response to the receipt of specific permutation signalsof the Baudot type, which are well known in the printing telegraph art,by the receiving magnets I3 or I4, mechanism in the respective selectivecontrol unit is actuated for performing a certain function or closing acertain contact. In the afore-identified Zenner patent, one such contactis depicted in Fig. 5 by the reference numeral IEI and as described inthe specification of that patent numerous contact assemblies similar tothe contact assembly IBI are provided which are actuated in response tovarious predetermined series of permutation signals.

The control center and control tower are provided respectitvely withconventional telegraph transmitters I5 and I! for transmittingpermutation signals over a line I8 connecting the two offices. It willbe understood that the remainder of the mechanism shown in the circuitdiagram is duplicated for each other level which is assignable to theaircraft.

When an airplane reaches a certain distance from the landing field thecontrol center operator closes an assign key I9 which corresponds to thelevel to which the airplane is being assigned. Closure of the assign keyI9 completes a circuit from positive battery, through a normally closedcontact 2I and armature 22 (the contact 2i and armature 22 being closedwhenever a slow-to-close line relay 23 is energized), over a lead 24,through a now closed swinger 26 and contact 27 through the assign key I3and its associated contact, over a lead 28, through the No. 8 contact ofa relay R2, over a lead 23, over a lead 3!, through a clutch operatingmagnet 32 in the transmitter is, to negative battery. Energization ofthe magnet 32 causes an operating shaft (not shown) in the transmitterI6 to commence rotating and an auxiliary cam 33, representedschematically in Fig. '7, and mounted on the operating shaft, moves aswinger 34 to a position whereby it makes with a contact 33. When theswinger 34 and contact 36 make in this manner, the circuit to theconductor 28 is extended over wo additional paths, namely: From theconductor 23, through the No. l contact of the relay R2, over a lead 3?,through a relay RI, over a lead as, through the closed Contact 36- andSwi er 34 the contact 54.

to negative battery; and from the conductor 28 through the R2 relay,over a lead 39, through a back contact [3 of the relay RI over a lead4!,

over the lead 38, through the closed contact 35 and swinger 34, tonegative battery.

while energization of the relay R2 causes its contacts Nos. I-E toclose. When the No. 6 contact of the relay R2 closes, a locking circuitis estab-' lished for the relay R2 from positive battery, through theclosed No. 6 contact of relay R2, through the relay R2, over the lead39, through the closed No. [4 contact of relay RI, to negative battery.When the No. I contact of the relay R2 opens, in response to theenergization of the relay R2, the original energizing circuit for therelay RI is broken; however, by the time that the No. I contact of therelay R2 opens, the No. II contact of the relay RI is closed so that therelay RI is closed and the relay RI is energized by a locking circuitfrom positive battery, through the No. I. I contact of the relay RI,through the relay RI, over the lead 33, and over the previously tracedcircuit to negative battery. Closure of the No. 12 contact of the relayRI, due to the energization of the relay RI, maintains the clutch magnet32 energized so as to cause the operating shaft (not shown) of thetransmitter It to continue to rotate.

As the transmitter operating shaft rotates, while the Nos. l-5 contactsof the relay R2 and Nos. 2, 4, 6, 8, and I0 contacts of the relay R5 areclosed, circuits are conditioned from the line I8, over a lead 42, overa lead 33, through the contacts Nos. I-5 of the relay R2, through straps44, through the contact Nos. 2, 4, 5, 8, and I8 of the relay RI, overthe leads 46, over a group of code wires 41, to a group of transmittingcontacts 48, 49, 50, 51, and 52. As the transmitter operating shaftrotates, a series of cams (also not shown) thereon sequentially closethe contacts 48, 49, 50, 5|, and 52 against the contact 54. The straps44 shown as. solid lines represent connections between the contacts ofthe relay R2 and of the relay RI, whereas the dotted lines representvbroken circuits between the contacts of the relays R2 and RI. The straps44 which are shown solid, are in circuit with the trans mitting contacts48 and 49, and therefore when the contacts 48-52 are closed sequentiallyagainst the contact 54, the line I8 will be closed as contacts 48 and 49close with contact 54 but open as the contacts 50, 5i, and 52 closeagainst This results in the tranmission of a permutation signal over theline It consisting of two current impulses followed by three noncurrentimpulses. According to the well known Baudot code such as signal is an Asignal. A contact 55, commonly known as a startstop contact, is incircuit with the line I8 and normally is closed against the contact 54to maintain the line l8 in an energized condition. When the transmitteroperating shaft rotates, the contact 55 opens from the contact 34thereby enabling the transmission of the permutation code signal.

By reference to Fig. '1 it will be apparent that upon the completion oftransmission of the five signal impulses comprising a permutation signalthe operating shaft of the transmitter IE will have nearly completed arevolution, at which time the auxiliary cam 33 functions to move theswinger 34 from engagement with the contact 36, Breaking the circuitbetween the swinger 34 and. the contact 36 breaks the locking circuit tothe relay RI through the No. II contact of the relay RI. Uponde-energization of the relay RI its contacts Nos. 2, t, 6, 8, III, II,I2, and It open While its contacts Nos. I, 3, 5, I, 9, and I3 close. Therelay RI is a slow to release relay and does not allow its armatures tofall back until the clutch magnet 32 has been energized sufficientlylong to start the operating shaft of the transmitter I6 on its nextrevolution; however, the RI relay does release its armatures prior tothe next closure of the swinger 34 against the contact-36, which isapparent from Fig. 7. When the operating shaft in the transmitter I6 isstarted it completes a revolution irrespective of the condition of theclutch magnet 32. As is also apparent from Fig. 7 the auxiliary cam 33closes the swinger 34 against the contact 36 very shortly after therelease of the armatures of the relay RI.

The opening of the No. I4 contact of the relay RI breaks the lockingcircuit for the relay R2, but at the same time as the No. It contactopens, the No. I3 contact of the relay R! closes. At this time theswinger 34 and contact 36 are open, however the relay R2 is a. slow torelease relay and before its armatures fall back, the swinger 34 closesagainst the contact 36 and thereby completes a locking circuit for therelay R2 from positive battery, through the No. 6 contact of the relayR2, over the lead 39, through the No. It contact of the relay RI, overthe lead AI, over the lead 38, through the closed contact 36 and swinger34, to negative battery.

The closure of the Nos. I, 3, 5, I, and il contacts of the relay RIconditions a new set of circuits to the transmitting contacts 48-52 fromthe line I3, over the leads 42 and i3, through the closed contacts I- ofthe relay R2, over a set of straps 55, through the closed contacts I, 3,5, I, and 9 of the relay RI, over the leads 45, over the code Wires 41,to the transmitting contacts 4852. It will be noted that the straps 56in the circuits between the Nos. I--5 contacts of the relay R2, and theNos. I, 3, 5, I, and 9 contacts are represented as solid for the firsttwo circuits and as dotted for the last three impulses which results inimpressing another A signal to the transmitting contacts l852.Therefore, as the transmitting shaft rotates through its secondrevolution an A signal is transmitted over the line I 8.

In summation thereof, it may be appreciated that the closure of theassign key results in the transmission of the signals AA over the lineI8. These signals AA are indicative of the altitude assigned to aparticular aircraft and are the result of the operation of the relays RIand R2 in controlling the transmitter It. It is to be understood thatsimilar circuits are provided at both the control center and controltower for controlling aircraft at many other altitudes; for example, ifaircraft are to be spaced in 1000 foot increments of altitude, aseparate control center is provided at both the control center and towerfor each 1000 foot level, hence for controlling aircraft flying from1000 feet to 1500 feet, circuits are utilized.

The signals AA are received by the selector magnet Id of the controltower selective control unit I2 and in response to these signals,mechanism in the selective control unit I2 causes a double swinger 5? tomove to its rightward position to close a contact 58. This movement ofthe swinger 51 conditions a circuit from positive battery, through thecontact 58, over a lead 59, through a red light BI, over a, lead 52,through a relay RI9, through the closed No. 3 contact of the relay RIB,over a lead 63, through a contact 64 and swinger 65, to negativebattery. The

contact 6 3 and swinger 66 are similar to the contact 36 and swinger 34in the transmitter I6, and at the present time are open.

When the swinger 57 moves to the right the circuit through a cancelbutton 61 is broken at a contact 68, thus making it impossible for thetower to cancel the assignment made by the control center. At the sametime that the circuit through the tower red light BI is conditioned thecircuit through the contact 58 and lead 59 is also extended over a lead69, through theNo. I contacts of relays R20 and RI 9, through the No. 8contact of a relay RI8, over a lead II, through a clutch operatingmagnet I2 (similar to the clutch operating magnet 32 in the transmitterI6) to negative battery. Upon energization, the magnet I2 releases anoperating shaft (not shown) in the transmitter I7 and a cam 33 (Fig. '7)closes the swinger 66 against the contact I54 thereby completing theafore-mentioned circuit through the red light BI and thereby causing itsillumination.

When positive battery is extended to the lead 69, as described above,circuits are also completed for energizing the relays RI1 and RI8. Theenergizing circuit for the relay RI I extends from the lead 69, over theNo. I contacts of the relays R20 and RIB, through the No. I contact ofthe relay RIB, over a lead I3, through the relay RII, over the lead 63,through the closed contact 64 and swinger 65 to negative battery. Theenergizing circuit for the relay RI8 extends from the lead 69, over theNo. I contacts of the relays R20 and RIB, through the relay RIB, over alead I4, through the No. I3 contact of the relay RII, over the lead 63,through the closed contact 64 and swinger 66 to negative battery. Uponenergization, the relay RII locks up over a circuit from positivebattery, through the No. II contact of the relay RI I, through the RIIrelay, over the lead I33, through the closed contacts and swinger 66 tonegative battery. Upon energization of both the relays RI1 and RI8 alockmg circuit is established for the relay RIB from positive battery,through the No. 6 contact of the relay RIB, over lead I5, through therelay RI 8, over the lead I I, through the No. I 6 contact of the relayRII to negative battery.

It will be noted that straps It connecting the Nos. I -5 contacts of therelay RI 8 with the Nos. 2, II, 8, 8, and [0 contacts of the relay I!are so arranged that an A signal will be impressed to a set oftransmitting contacts 17, I8, 79, 86, El, during the first revolution ofthe transmitter operating shaft (not shown) in the transmitter IT. A setof straps 83, connecting the Nos. I-t: contacts of the relay RI3 withthe Nos. I, 3, 5, I, and 9 contacts of the relay RI1, are so arranged asto cause a B signal to be impressed to the transmitting contacts 'I1-8I.The operation of the relays RI! and RI8 and their associated armaturesis identical with the operation of the relays RI and R2 and therefore itis not believed necessary to describe the details further as to how therelays RI and R2 cooperate with the transmitter I7 to enabletransmission of the signals AB over the line I8.

Upon illumination of the tower red light 6!, that is, when the operatingshaft commences rotating in the transmitter H, the relay RIQ becomesenergized. Upon energization, the relay Hi9 pulls up its armaturesthereby breaking the circuits through its Nos. i and 3 contacts andestablishing a locking circuit for itself from negative battery throughthe No. 2 contact of the relay RIB, through the relay R19, over the lead62, through the red lamp 6|, over the lead 59, through the closedcontact 58 and swinger E1, to positive battery. The contact swinger El,when moved. to its rightward position, remains in such position until adifferent special signal combination is received to cause it to moveback to its leftward position, and consequently the tower red light 6!remains illuminated until such a special signal is received on theselector magnet M of the selective control unit l2.

The signals AB, transmitted over the line 18 by the transmitter IT, arereceived by the selector magnet [3 in the selective control unit H, andin response to the signals a swinger 84 is moved against a contact 86.When the swinger 84 closes against the contact 86 a circuit is completedfrom positive battery, through the closed swinger 84 and contact 86,over a lead 81, through a green light 83, over a lead 39, through aresistance 9!, to negative battery. The green light 88, which is locatedon the control center display board is thereupon illuminated indicatingto the control center that an assignment has been made by the controlcenter for the particular level. If for some reason the green light 38will not operate, due perhaps to the fact that the light is burned out,a circuit is completed from the lead 81, over a lead 92, through a relayR52, through the resistance 91 to negative battery. The relay BIZ, uponbeing energized, pulls up its armature and closes its No. I contactthereby completing a circuit from positive battery, through the No. 1contact of the relay RI 2 to an alarm (not shown) of any well knowntype. Whenever the alarm operates the operator is informed that anassignment has been made and that the light is inoperative.

The red light 6| at the tower is also provided with an alarm circuitoperable upon failure thereof to illuminate when energized. A highresistance relay R20 is normally shunted out by red lig t %I, however,if the red light i burns out a circuit is established which by-passesthe light, from the lead 69, through the relay R28, through the relayRlfi, through the No. 2 contact of the relay RIG, (which contact will beclosed at this time) to negative battery. The relay R26, upon beingenergized, closes its No. 2 contact to thereby complete a circuit frompositive battery, through the No. 2 contact of the relay R25, through analarm light 93, to an alarm of any well known type. The operation of thealarm calls the attention of the operator to the fact that one of thedisplay lamps is inoperative and the light 93 informs him which one isinoperative When the lamp 5! is burned out, the relay R20 is rapid inpulling up its armatures and therefore when its No. contact is opened,the energizing circuit for the clutch magnet 12 is not established for aduration sufficient to permit the start of a rotation of the operatingshaft of the transmitter 12. As a consequence the AB signal is nottransmitted back to the control center and therefore neither the centergreen light 88, nor the center alarm is operated. The center operatortherefore is informed that something is wrong at the control tower andthe control tower operator, due to the alarm thereat 8 and also due tothe illumination of the lamp 93, also knows that the light 6| isinoperative. The necessary steps will then, of course, be taken tocorrect the diificulty.

Assuming that the control center has assigned a level to an airplane aspreviously described and that the tower wishes to take over control ofthat level, the tower operator then closes an assign key 94 for thatparticular level. If there are no signals being transmitted over theline It at the time when the assign key 94 is closed, a slowto-closeline relay 9B is closed, and a circuit is completed from positivebattery through a contact 91; through a pulled up armature 98 of therelay 96, over a lead 99, over a lead lill, through the assign key 94,over a lead I02, through a No. 8 contact of a relay R14, over a leadH33, over the lead H, through the clutch magnet 12, to negative battery.The energization of the clutch magnet 12 enables the transmitteroperating shaft in the transmitter ll to start rotating and at this timethe relays R13 and R54 cooperate with the transmitter I! to transmit thesignals AC over the line 18. Since the operation of the relays Hi3 andRM, in enabling the transmission of the signals AC by the transmitter H,is identical with the operation of the relays R! and R2 in enabling thetransmitter H3 to transmit the signals AA, the details of the operationof the relays R13 and RM will not be described. It should be noted theNos. I--5 contacts of the relay RM are strapped to the Nos. l-I 0contacts of the relay RI 3 in a manner such that the transmitter l1transmits the signals AC upon the operation of the relays R13 and RM.

The signals AC are received by the selector magnet 13 at the controlcenter and actuate the selective control unit I l in a manner wherebythe swinger 84 is moved to its leftward position (as shown) to therebybreak the circuit to the green light 83 at the control center. Also inresponse to the signals AC a contact swinger I04 is moved to itsrightward position in engagement with a contact I06 and this conditionsa circuit from positive battery, through the swinger I04 and contactI86,- over a lead {01, through a red light I88 (corresponding to thesame level as that of the green light 88) over a lead I09 through therelay RIG, through the No. 3 contact of the relay RIB, over a lead lil,over the lead 38, through the contact 36 and swinger 34 (presentlyopen), to negative battery. Another circuit is established at this timewhen positive battery is extended through the swinger I04 and contactH36, over the lead I01, over a lead H2, through the No. I contact of arelay Bi i, through the No. I contact of a relay Rle, through the No. 8contact of a relay R9, over a lead H3, over the lead 3|, through theclutch magnet 32, to negative battery. Energization of the clutch magnet32, as usual, starts the transmitter operating shaft rotating, whereuponthe swinger S4 closes against the contact 36 to thereby complete theenergizing circuit for the red light H38. When the clutch magnet 32 isenergized the relays R8 and R9 are also energized, in the manner alreadydescribed with reference to the relays RI and R2. The Nos. l--5 contactsof the relay R9 and the Nos. I-l0 contacts of the relay R3 are sostrapped as to enable the transmission of the signals AD by thetransmitter Iii during the operation of the relays R8 and R9.

Upon completion of the circuit through the lamp 33, the relay Rifl pullsits armatures and establishes a locking circuit for the red light cuitconnected to an alarm (not shown).

I03 from positive battery, through the closed swinger I04 and contactI06, over the lead I I11, through the red light I08, over the lead I09,through the relay RIO, through the No. 2 contact of the relay RI E1, tonegative battery.

When the signals A are received by the selective control unit II, theswinger 26 also is actuated in response thereto and caused to move toits rightward position This movement of the swinger 26 breaks thecircuits to the assign key I9 and to a cancel key H4 at the controlcenter thus making it impossible for the control center to gain controlof the level at this time.

If the red light I08 is burned out a circuit is established frompositive battery, through the closed swinger I04 and contact I06, overthe lead It'I, over the lead H2, through a high resistance relay RI I,through the relay RID, through the No. 3 contact of the relay RIO, 'overthe lead II I, over the lead 38, through the closed contact 38 andswinger 34, to negative battery. When the relay RIO becomes energizedand pulls up its armatures it closes its No. 2 contact to therebycomplete an obvious locking circuit for itself and for the relay RI I.The relay RI I, upon being energized opens its No. I contact and closesits No. 2 contact. Opening of the No. I contact of the relay RII breaksthe initial energizing circuit to the clutch magnet 32 to therebyprevent successive rotations of the transmitter operating shaft of thetransmitter I6 after the transmission of the signals AD. Closure of theNo. 2 contact of the relay RII completes an obvious circuit to an alarmto thereby warn the center operator that the light is inoperative.

The AD signal, upon being transmitted over the line I8 is received bythe selector magnet I4 at the tower. In response to this AD signal aswinger I I6 is caused to move to the right against a, cooperatingcontact H1 to thereby complete a circuit from positive battery, over alead H8, through the swinger H6 and contact II1, over a lead H9, througha green light I2I, over a lead I22, through a resistance I23, tonegative battery. Normally the green light I2I is illuminated at thistime; however, if it is burned out a circuit is established from thelead H9, over alead I24, through a high resistance relay R2 I, throughthe resistance I23, to negative battery. When the green light I2Iilluminates, the circuit through the relay R2I is shunted out. Uponenergization of the relay R2I it closes its No. I contact and therebycompletes a circuit from positive battery through the No. I contact ofthe relay RZI, through an alarm light I26,to a cir- Thus, when the greenlight I2I fails to illuminate the alarm attracts the attention of thetower operator and the alarm light I2I informs the operator which greenlight is not functioning.

Also, when the selector magnet I4 receives the signals AD, the doubleswinger 51 in the selective control unit I2 is caused to move to itsleftward position (as shown) thereby extinguishing the red light 6| andconditioning the circuit to the cancel button 61. At this time the towercontrols the assigned level, and assuming that the lights arefunctioning properly this fact is clearly indicated at both the controlcenter and control tower due to the illumination of the red light IE8 atthe control center and of the green light i2I at the control tower.

As a plane descends during its landing procedure it leaves its assignedlevel and the tower operator cancels the assignment by actuating thetower cancel button 61 for that particular level. Under the existingcondition of the circuits, depression of the tower cancel buttoncompletes a circuit from positive battery, through the closed contact 91and swinger 98 (closed when there is no transmission taking place overthe line I8 to cause the de-energization of the relay 98), over the lead99, through the double swinger 51 and contact 68, through the cancelbutton 61 and its operating contact, over a lead I21, through the No. 8contact of the relay RIG, over a lead I28, over the lead II, through themagnet 12, to negative battery. As soon as the clutch magnet 12 releasesfor rotation the operating shaft in the transmitter I1, the cam 33 onthe operating shaft closes the swinger 66 against the contact 64 andcompletes momentary circuits for the relays RIB and RIG extending fromthe lead I21, through the No. 1 contact or" the relay RIG, over a leadI29, through the relay RI5, over the lead 63, through the closed contact6A and swinger B6 to negative battery; and also from the lead I21,through the relay Rlt, over a lead I3I, through the No. I3 contact ofthe relay RI5, over a lead I32, over the lead 63, through the closedcontact 64 and swinger 65 to negative battery. The Nos. IIIB contacts ofthe relay RI5 are so strapped to the Nos. I5 contacts of the relay RIGas to enable the impression of the signals AE to the transmittingcontacts 11-8I. When the relays RI5 and RIG are energized, thetransmitter I1 cooperates therewith in the identical manner that thetransmitter I6 cooperates with the relays RI and R2, in order to enablethe transmission of the signals AE over the line I8.

The signals AE are received by the selector magnet I3 and cause theswinger 26 to move to its leftward position (as shown) and also causethe swinger I04 to move to its leftward position (as shown) intoengagement with a contact I33. Restoration of the swinger 26 to itsleftward position against the contact 21 enables the control center toagain assign the particular level to another plane. Restoration of theswinger I @4 to its leftward position against the contact I33, breaksthe circuit to the red light I88, and completes a circuit from positivebattery through the swinger I04 and contact I33, over a lead I34,through the N o. I contact of the relay R1, through the No. 8 contact ofthe relay R6, over a lead I36, over a lead 3|, through the clutch magnet32 to negative battery. The transmitter operating shaft in thetransmitter I6 starts to rotate at this time and upon closure of theswinger 3 3 against the contact 36 by the auxiliary cam 33, a circuit isextended from the lead ltd, through the relay R1, through the No. 3contact of the relay R1, over a lead I31, over the lead 38, through theclosed contact 36 and swinger 34, to negative battery. The relay R1 isslow to operate, and at this same time a circuit is also establishedfrom the lead I 34, through the No. I contact of the relay R1, throughthe No. '8 contact of the relay R6, over a lead I38, through the relayR5, over a lead 38, through the closed contact 36 and swinger 34, tonegative battery; and another circuit from the lead E34 is established,through the No. I contact of the relay R1, through the relay R6, over alead 539, through the No. I3 contact of the relay R5, over the lead I31,over the lead 38, through the closed contact 36 and swinger 34, tonegative battery.

The Nos. I-I0 contacts of the relay R5 and the Nos. I5 contacts of therelay R6 are strapped together in a manner to enable the relays R and Reto cooperate with the transmitter it to transmit the signals AF. Therelay RT, being slow to operate does not pull up its armatures untilafter the transmission of the signals AF. The relay R's is necessary inorder to prevent transmission of more than a single sequence of thesignals AF, as the swinger IE4 and contact I33. remain closed whenclosed in response to the signals AE. When the relay R'I pulls up itsarmatures its No. I contact and No. 3 contact are opened which break thecircuits to the relays R5 and RS, and its No. 2 contact is closedthereby completing its own locking circuit from the lead I34, throughthe relay R'I, through the No. 2 contact of relay R1, to negativebattery.

Upon receipt of the signals by the selector magnet I4, the swinger He inthe selective control unit I2 is moved to the left (the position shown)which opens the circuit through the swinger H6 and contact Ill; Breakingof this circuit ale-energizes the green light i2I and therefore alllights are extinguished for the particular level and all circuits forsuch level are in condition for a new assignment of a plane to thatlevel.

When an airplane merely flies through the area controlled by the controlcenter and does not land at the airport within the area it becomesnecessary that the center be able to assign an altitude to the plane andlater, when the plane leaves the control zone, to cancel the assignment.This is accomplished in the following manner:

The plane isassigned an altitude as before described, at which time thecontrol center operator depresses his assign hey I5 corresponding tothat level. The center equipment transmits the signals AA over the lineit, as before, such signals being received by the selector anagnet I4 atthe tower. The tower red light (El is illuminated in response to thesignals AA and the tower transmitter I1 is caused to transmit thesignals AB over the line I8. The A13 signals cause the illumination ofthe center green light '83. Control over the plane belongs to thecontrol center which retains control thereover until the plane leavesthe controlled area.

At the time when the plane leaves the area, the center operatordepresses th cancel button I14 for the particular level which (assumingthat no 'signals 'are being transmitted over the line I8 at this time)completes a circuit from positive battery, throughthe contact 2I andswinger 22,

over the lead 2'4, through the closed swinger 28 and contact 26, throughthe cancel button H4, over a lead I'M, through the No. 8 contact of therelay R4, over a lead I42, over the lead 3!, through the clutch magnet32, to negative battery. The operating shaft of the transmitter is,being actuated upon the energization of the clutch magnet 32, causes thecam 33 to close the swinger 34 against the contact 35, therebycomplating energizing circuits for the relays R3 and R4. The energizingcircuit for the relay R3 extends from the lead I'M, through the No. lcontact of the relay R4, over a lead M3, through the relay R3, overthelead '38, through the closed contact 36 and swinger 3d, to negativebattery. The energizing circuit for the relay Rd extends from the leadI'M, through the relay R 1, over a lead I44, through the No. I3 contactof the relay -R'3,'over the -lead 38, through the closed contact 36'andswinger-34x0 negative battery. The Nos. IIIl contacts of the relay R3are strapped to the Nos. I- -5- contacts of the relay as so as. toenable the transmitter I6 to'transmit the signals AG over the signallineI8 at this time. in the same manner as the relays RI and R2 cooperatewith the transmitter 5 to transmit the signals AA.

The signals AG- are received on both selector magnets I3 and II. Inresponse. to the AG signals the swinger 84 in. the selective controlunit II moves to the left (the position shown) thereby breaking thecircuit tothe'center green light 38. The AG signals also cause theswinger Hi l, in the center selective control unit It, to move to theright to complete, the heretofore traced circuitsto the. center redlight I53 and; to the relays RB and R9. The relays R8 and R9 operate inthe same manner, as described before, in cooperation with thetransmitter ifito cause transmission of the signalsFAD over the signalline 18.

When the selector magnet I l in the tower selective control unit I2receives, the signals AG immediately followed by the signals AD aswinger I45 is moved to the right momentarily to engage a contact Hi1.This completes a circuit from positive battery, over the lead H8,through the closed swinger I 46 and contact i li over a lead I48, overthe lead I21, through theNo. 8 contact of the relay RI'fi, over the.lead I28, over the lead H, through the clutch ma net "12, to negativebattery. Upon the, start of rotation of the transmitter operating shaftin the transmitter Il, the cam 33c1oses, the swinger Giiagainst thecontact 64, thereby completing momentary circuits .to the relays HA5:andRIS. The relays Rt 5 and R I 5 then cooperate with the transmitter53 in the manner hereinbefore described-to enable the transmitter If? totransmit the signals A'E over the line: I8.

The. AD? signals of the AG-Al3f combination also cause the, doubleswinger El move to the-left to restore the; tower cancel button 57 tooperable condition, and to break the circuit to. the tower redlightxfiyl; The AD .s-ignalslalso cause the swinger 116 to move'tc theright to cause illumination of the tower green light Lilli in the manneralso hereinbefore described.

The .AE signal; combination, transirritted over the line 13 bytheytransmitter ll, due to thencoperation or" the relays R-I j and it,is received by the center selector magnet i3 and causeslthe swinger itsthey-selective control Iii, to move to the left therebybreaking itsconneuion with the contact tee; and making-with the contact 93-3.'Whenthe-circuit through the-swinger 13 2-. and contact M35 is brokenthe center'red light we isextingnished and the locking circuit for.thesrelays R18 and RH is broken which restores these relays to theirnormaldeaenergized condition. When the swinger it l-engages the contact:133 acircnit is extended from positive battery, through theswingerlfirhand contact 133, and over the .lead,zl3. l to the relays Ridand R!These .relayszcooperate :with the transmitter It in the manner alreadydescribed to cause transmission of the-signalsfirrii over thelinelil.

The AP .s'ignals. are received by the selector magnet (I -'i and causethe-swinger- I-ifi the sale"- tive control I2 to .mov.e to the 'leittobreak the obvious circuit. 2130 the. tower green light in the manneralready described. Theneforeatthis time all lights for the particularlevel are restored to normal extinguished-condition.

When a plane .under the control oi-the tower descends to a lower level,as in the case of a 13 landing operation, it is necessary that the towerbe able to assign the plane to the new altitude. This is accomplished inthe following manner.

The operation whereby the tower operator cancels the assignment of anassigned level has already been described. When the tower operatorwishes to assign a new level to an airplane, he depresses the assignbutton 94 corresponding to the level which is to be assigned. Thiscompletes a circuit from positive battery, through the contact 9! andarmature 98, over the lead 99, through the assign button 94, over thelead Ill-2, to the relays Hi3 and RM, and to the clutch magnet '12. Therelays Hi3 and RM cooperate with the transmitter H in the usual mannerto transmit the signals AC over the line [8. The AC" signals arereceived by the control center selector magnet 53 and cause illuminationof the red light N38 for the new level and initiate transmission of thesignals AD by the transmitter l6 under the control of the relays R8 andR9. ihe signals AD are received by the selector magnet i l in the towerselective control unit [2 and cause illumination of the tower greenlight I25. At this time a new level has been assigned and, as isindicated by the condition of the lights, is under the control of thetower.

When the signals AC were received by the center selector magnet l3, theswinger 26 also moved to the right, thereby cutting out the cancelbutton I M and assign button 9 at the center. Thus it is impossible forthe center to cancel an assignment made by the tower. The tower,however, can cancel this new assignment, as the AD signals transmittedfrom the center cause the double swinger in the tower selective controlunit E2 to move to the left. As is obvious, when the double swinger 57is closed with the contact 68, the tower cancel button 61 is operable.

In the above description of the invention and in the drawings, only thecontrol circuits for transmitting signals indicative of a singlealtitude are shown and described. It will be remembered that inpracticing the invention there are provided substantial duplicates ofthese control circuits for each altitude to which it is desired toassign airplanes. Also in actual practice of the present invention the Aseries of signals, which has been described, is used for only one level,whereas the signals for other levels might be a B, C, etc. series ofsignals. To change from the A series of signals merely involves changingthe strappings between the control contacts of each pair of controlrelays, such as Bi and R2. The selective control unitswould haveswingers and contacts for each level like those shown, but the swingerswould respond only to signals which control mechanism associated withthe particular level.

It is contemplated that numerous changes and modifications may be madein the invention without departing from the scope thereof.

What is claimed is: 1. In an aircraft altitude control system, a paircolored lights corresponding to the assigned altitude on the indicatorboard at said other station, other means at said other stationresponsive to said series of permutative signal impulses fortransmitting a second series of permutative signal impulses to saidfirst station, and means at said first station responsive to said secondseries of permutative signal impulses for illuminating the light of theother color corresponding to the assigned altitude on the indicatorboard at said first station.

2. In an aircraft altitude control system, a pair of control stations,an indicator board at each of said stations having a pair of differentcolored lights corresponding to each altitude at which aircraft may beassigned, means at each of said stations for assigning an altitude to anaircraft including means for transmitting a series of permutative signalimpulses to the other station indicative of the assigned altitude, meansat said other station responsive to said series of permutative signalimpulses for illuminating one of said lights corresponding to theassigned altitude on the indicator board at said other station, othermeans at said other station responsive to said series of permutativesignal impulses for transmitting a second series of permutative signalimpulses to said first station, means at said first station responsiveto said second series of permutative signal impulses for illuminatingthe light of the other color corresponding to the assigned altitude onthe indicator board at said first station, said station having the lightof said other color displayed thereat having control of the assignedaltitude, and means operable at said station displaying the light ofsaid other color for canceling the assignment and extinguishing alllights for the assigned altitude.

3. In an aircraft altitude control system, a pair of control stations,an indicator board at each of said stations having lights correspondingto each altitude at which aircraft may be assigned, means at each ofsaid stations for assigning an altitude to an aircraft including meansfor transmitting a signal to the other station indicative of theassigned altitude, means at said other station responsive to said signalfor illuminating the light corresponding to the assigned altitude, alarmmeans at each of said stations, and normally ineifective means at eachof said stations for actuating said alarm means rendered effective inresponse to said signal upon a failure of the light corresponding to theassigned altitude.

4. In an aircraft altitude control system, a pair of control stations,an indicator board at each of said stations having lights correspondingto each altitude at which aircraft may be assigned for indicating anassigned altitude, means at each of said stations for assigning analtitude to an aircraft including means for transmitting a signal to theother station indicative of the assigned altitude, an indicator circuitfor each of said lights, means at said other station responsive to saidsignal for actuating the indicator circuit of the light corresponding tothe assigned altitude, alarm means for indicating a failure of saidlights to indicate the assigned altitude, and means controlled by thereception of a signal and the resistance of said indicator circuit ofthe light corresponding to the assigned altitude for controlling saidalarm means.

5. In an aircraft altitude control system, a control center having asignal transmitter thereat, a control tower having a signal transmitterthereat, a separate selectivereceiving apparatus c uitsadapted to be sent ansmitter operationf said signal 15 at both the control center andtower, a plurality of pairs of control cireuit's a dapted to bepermutati-vely connected to' thece'rlter transmitter, a second pluralityof pairs ofcontrol circuits adapted to be permutatively'connected to thetower transmitter, a signalling channel interconnecting the transmittersand selective receiving apparatus, means at the center for selecting andsuccessively connecting one pair of thecenter pairs of control circuitsto the transmitter and for simultaneously initiating operation of saidtransmitter to transmit over said signalling channel a pair of signalsas determined by the permutative connections .of said pair of centercontrolcircuits, means actuated by the reception of said center pair ofsignals at the tower selec- -tive-receiving apparatus .for selecting andsuccessively connecting one of said pairs of tower con.- trol circuitsto said tower transmitter and for simultaneously initiating operation ofsaid tower transmitter-to transmit over said signalling channel a pairof signals as .determinedhy the permutativeconnection of said pair oftower COX]: trolcircuits, and means at both thecontrolcenter and .toweroperated .by the respective selective receiving apparatuses -.forindicating reception of a pairofrsignalsby the particularseleetivereceiving apparatus.

-6. In an aircraft altitude control system, a

controlcenter having asignal transmitterthereat, a control vtower havingalsignal transmitter thereat, a pairof control circuits adapted to .bepermutatively connected to .said center transimittena secondpairorcontrolcircuits adapted to be permutatively connected .to said towertransmitter, .each of said controlcircuits being adapted to control .thetransmitter to transmit a permutative series of signal impulses in ac,-cordance withwthe permutative connection, oirthe controlcircuits,.vmeans-at the control center for sequentially connecting eachofthe center control circuits to said. center -.transmitter, meansoperated by said last mentionedmeans for lini- --tiating theoperationofrsaid center transmitter to transmit two series of permutativesignalim- 'pulses means at saidwcontroltowerlresponsiveto saidtwo-series .ofpermutative impulses foresequentially connecting eachofthe tower. control circuits tosaid tower transmitter, meansoperating-bysaid last-mentionedmeans rior initiatin operation of saidtower transmitter to transmit two series of permutative signal-impulses,indicator means at b oth thecontrol center and towenand means operatedby thereception of said series of signal impulses at both thercontrolcenter andtower ior actuating each. of said indicator means.

'7. In an aircraft altitude control system, .a control center-having-asignal transmitter'thereat, a control tower-havinga signal transmitterthereat, a selective --control unit responsive to permutative signals atboth'the-control. center and tower, asing-le signalling channelinterconnecting'the signal transmitters and selective controlunits,-aplurality of permutatively difierent control circuits adaptedto-be permutativelyconnected to the control center signal transmitter,a'plurality of permutatively di-fierent controlcirpermutativelyconnecteclto the control towersignal transmitter means at,

the control center for selecting a predetermined one of 5 controlcenter; control circuits and connecting said selected circuit to thecontrol center a said "means also initiatihg transmitter to transmit asignal in accordance with the permutatiye con: nection of its controlcircuit, means operated by the reception or" the signal at the controltower selective control unit for connecting a predetermined one of thecontrol tower control circuits to the control tower signal tran mitter,said last mentioned means also initiating operation of the control towersignal transmitter to transmit a signal in accordance with thepermutative connection' of its control circuit, indicator means at boththe control center and tower aQtuated by reception of signals at each ofthe selective control units, means at said control tower for connectinganother of said control tower control circuits to the control towersignal transmitter, said last'mentioned means initiating operation ofsaid control tower signal transmitter to transmit a signal in accordancewith the permutative connection of its control circuit, means operatedby the reception of the signal at the control center selective controlunit for connecting another of said plurality of control center'controlcircuits to the control center signal transmitter, said .last mentionedmeans initiating operation of said control center signal transmitter totransmit a signal in accordance with the permutative connection of itscontrol circuit, and additionalil dicator means operate'diby thereceptionofth'ese last mentioned signals at each of the seleQtivecontrol units.

8Q in an aircraft altitude controlsystem, a pair of controlstat-ionsfa'n indicator-board at eachof said stations having alight ofafirst color and a light of a second color,.means at each station fortransmitting a first series Ioipermutative sig al impulses to theother'statio'n, .means at saidother tive signal impulsesior'illuminating' the light of the first color, means atsaid otherstationalso responsive to the reception of said firstseries ofpermutative signallimpulses for transmitting a second series .ofpermutative signal impulses ,to

said first station, means at said first station responsive to saidsecond series of permutative signal impulses for illuminating the lightof the second color, means at the station displaying the light of thesecond color for transmitting'a third series of permutativesignalimpulses to, said other stat ion,'means responsive to said thirdseriesof permutative signal impulsesforl extinguishing the light .of thefirst color, means at said others'ta- 'tion responsive to the receptionof the third series of permutative signal impulses for transmitting afourth series of permutative impulses, and means at saidiirst stationresponsive tosaid fourth series of permutative signal impulses forextinguishing said light at the secondcolor.

' 9. :In'a.telegraphcontrolsystem, afirst station having a telegraphtransmitter thereat, aisecond station having a telegraph transmitterthereat', a

pair of. ccntrolcircuits adapted to be connected to thetransmitter atthelfirst station, a pair of control circuits adapted to beconnected to.the transmitter at the second station, are'lay for controlflingwhichcontrol ciricuitis to heconnected to the transmitter at the firststation, a relay for controlling which control. circuit is to beconnected to the transmitter at, the second station,

means at the first stationior energizing therelay .thereat to connect afirstone of the control circuits to the transmitter. to cause thetransmitter r. to generate alfirst. series of impulsesindicative of theconnected control circuit, means operated by the transmitter forreleasingtherelay at thev first .station to. connect thesecond controlcircuit of vthe:

pair thereat to the transmitter to cause the transmitter to generate asecond series of impulses indicative of the connected control circuit,means at the second station responsive to the reception of both seriesof impulses for energizing the relay at the second station to connect afirst control circuit of the pair to the transmitter thereat, said meansbeing also effective to initiate the transmitter at the second stationinto operation to generate a first series of impulses as determined bythe control circuit connected thereto, and means controlled by thetransmitter at the second station for ole-energizing the relay toconnect the second control circuit of the pair to the transmitter tocause the transmitter to generate a second series of impulses asdetermined by the control circuit connected thereto.

10. In a telegraph control system, a first station having a transmitterthereat, a plurality of first control circuits associated with the firsttransmitter, a first selective control unit associated with the firstcontrol circuits, a second station having a transmitter thereat, aplurality of second control circuits associated with the secondtransmitter, a second selective control unit associated with the secondcontrol circuits, means for manually operating the first selectivecontrol unit to select and connect a predetermined one of the firstcontrol circuits to the first transmitter, means operated by the firstselective control unit for initiating the first transmitter intooperation to transmit a first signal as determined by the controlcircuit connected thereto, said second selective control unit adapted torespond to said first signal to select and connect a, predetermined oneof the second control circuits to the second transmitter, means operatedby the second selective control circuit for initiating the secondtransmitter into operation to transmit a second signal as determined bythe control circuit connected thereto, means for manually operating thesecond selective control unit to select and connect a predetermined oneof the second control circuits to the second transmitter, means operatedby the second selective control unit for initiating the secondtransmitter into operation to transmit a third signal as determined bythe control circuit connected thereto, said first selective control unitadapted to respond to said third signal to select and connectpredetermined ones of the first control circuits to the secondtransmitter, means operated by the first selective control unit forinitiating the first transmitter into operation to transmit a fourthsignal as determined by the control circuit connected thereto, means forprecluding the operation of the manual means at the second station whenthe manual means at the first station is operated, and means forprecluding the operation of the manual means at the first station whenthe manual means at the second station is operated.

11. In a telegraph control system, a first station having a telegraphtransmitter thereat, a plurality of permutative control circuitsassociated with the transmitter at the first station, a, second stationhaving a telegraph transmitter thereat, a plurality of permutativecontrol circuits associated with the transmitter at the second station,means for selecting and connecting one of the circuits at the firststation to the associated transmitter, means operated by the selectingmeans for initiating the connected transmitter into operation totransmit a first permutative signal as determined by the permutativeconnection of the first control circuit, means at the second stationresponsive to said first signal for selecting and connecting apermutative control circuit to the transmitter located thereat, means atthe second station actuated by the selecting means for indicating thereception of said first signal, means operated by the selecting meansfor initiating said transmitter into operation to transmit a secondpermutative signal as determined by the permutative connection of thecontrol circuit, means at the first station responsive to said secondsignal for indicating the reception of the second signal, means at thefirst station for selecting another of the control circuits andpermutatively connecting it to the associated transmitter, meansactuated by said selecting means for initiating the transmitter intooperation to transmit a third sign-al as determined by the permutativeconnection of the control circuit, said selective means at the secondstation disrupting the indicating means upon reception of the thirdsignal, said selecting means also connecting another of the permutative,control circuits to the transmitter, means operated by the selectingmeans at the second station for initiating the transmitter intooperation to transmit a fourth signal as determined by the permutativeconnection of the control circuit, said selective means at the firststation disrupting the indicating means thereat upon reception of thefourth signal.

FRANK MARTINDELL.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date Re. 20,462 Kleinschmidt Aug. 3, 1937 1,616,186 Harlow Feb. 1,1927 1,620,704 Vencill Mar. 15, 1927 2,216,610 Culbertson Oct. 1, 19402,268,240 Brixner Dec. 30, 1941 2,344,760 Wight et al Mar. 21, 19442,425,973 Wight et al Aug. 19, 1947 2,529,596 Coley Nov. 14, 1950

